Mu problem
In theoretical physics, the μ problem is a problem of supersymmetric theories, concerning with understanding the parameters of the theory.
The supersymmetric Higgs mass parameter μ appears as the following term in the superpotential: μHuHd. It is responsible for the electroweak scale and should have the same order of magnitude, many orders of magnitude smaller than that of the planck scale, which is the natural cutoff scale. The soft supersymmetry breaking terms should also be of the same order of magnitude as the electroweak scale. This brings about a problem of naturalness: why are these scales so much smaller than the cutoff scale yet happen to fall so close to each other?
In gravity-mediated supersymmetry a proposed solution is that this term does not appear explicitly in the Lagrangian, because it violates PQ symmetry, and can therefore be created only via spontaneous symmetry breaking of this symmetry, which happens together with supersymmetry breaking, if supersymmetry breaks via an F-term, with the spurious field X (meaning that FX is the nnon-zero F-term), assuming that the Kahler potential includes terms of the form f(X)HuHd for some function f.